This invention relates generally to motor position estimation systems and in particular to motor position estimation systems for permanent magnet synchronous motors.
Permanent magnet synchronous motors (PMSMs) have become increasingly popular in high-performance variable-frequency drives due to their high efficiency, high torque-to-inertia ratio, rapid dynamic response, and relatively simple modeling and control. To achieve the proper field position orientation in motion control applications, it is necessary to obtain the actual position of the rotor magnets. Typically, this position is obtained through the use of position sensors mounted on the motor shaft. These position sensors can include a shaft encoder, resolver, Hall effect sensor, or other form of angle sensor. These sensors typically are expensive, require careful installation and alignment, and are fragile. Accordingly, the the use of these position sensors both in terms actual cost to produce the product and in the costs associated with the maintenance and repair of these systems is high.
Sensorless position estimation systems have been developed to overcome these limitations, but the present sensorless position estimation systems have their own drawbacks as well. These systems typically fall into two categories: back emf methods and signal injection methods. Back emf systems use the measured back emf voltage to estimate the position of the rotor magnets. The back emf voltage signal is roughly proportional to the rotational velocity of the motor. Although this method achieves valid results at higher rotational velocities, at low rotational velocities and high torque settings, the back emf voltage signal decreases to values that are too small to be useful, and vanish entirely at speeds close to a standstill. Thus, the back emf method is not suitable for these low rotational velocity high torque applications. The second method is the signal injection method in which an auxiliary signal is introduced into the motor electrical subsystem and measure the response of the motor electrical subsystem to estimate the rotor position. Although this method avoids the singularities of the back emf method, these methods are computationally intensive and thus are not well suited for industrial applications.
Accordingly, it would be advantageous to provide a position estimation system that avoids the singularities at low speeds and the computationally intensive methods of the prior art.